System comprising a pump, an injector and a regulator, with control signals to the pump which are based on calculated hose rigidities

ABSTRACT

A pump system that includes a pump, an injector and a regulator with a calculation unit. The regulator controls the pump to pump a liquid through a hose to the injector which opens and closes in response to an injector control signal, the time for an opening and closing cycle being called injector cycle and designated T s , and the injector&#39;s open period being designated γ. The injector has a pressure sensor to measure the pressure of the liquid in the injector and to deliver to the calculation unit a pressure sensor signal representing the pressure amplitude in the injector. The calculation unit calculates the hose&#39;s rigidity B as a function of measured pressured amplitudes A in the injector, the injector cycle T s  and the injector&#39;s open period γ, and the regulator determines the basis of B the control signal to the pump.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a 35 U.S.C. §§371 national phase conversionof PCT/SE2011/050386, filed Apr. 1, 2011, which claims priority ofSwedish Application No. 1050341-5, filed Apr. 8, 2010, the contents ofwhich are incorporated herein by reference. The PCT InternationalApplication was published in the English language.

FIELD OF THE INVENTION

The present invention relates to a pump system, and a method pertainingto a pump system. More specifically, a system and a method are indicatedfor automatically identifying the rigidity of a pressure hose.

The invention is described below on the basis of examples related to thevehicle industry, e.g. an SCR system and a fuel injection system, but isgenerally usable also for other applications pertaining to pressureregulation.

BACKGROUND TO THE INVENTION

So-called SCR (selective catalytic reduction) systems are used forreducing nitrogen oxides (NOx) from the exhaust gases of a dieselengine. Nitrogen oxides are thus converted, by means of a catalyst, tonitrogen gas (N₂) and water. A gas reductant, e.g. anhydrous ammonia,water-dissolved ammonia or urea, e.g. AdBlue, is added to a flow of fluegases or exhaust gases and is absorbed by a catalyst. Carbon dioxide isa reaction product when urea is used as reductant.

Using the SCR system involves injecting, for example, AdBlue at highpressure into the flue gases by means of an injector. A regulator isused to regulate the pressure in a high-pressure hose connected to theinjector. The system regulated comprises a pump, hoses and an injectorwith a pressure sensor. The amount of gas reductant (AdBlue) addeddepends inter alia on measured contents of nitrogen oxides, preferablymeasured downstream from where the injector is situated. The gasreductant is added by opening and closing the injector, the amount ofgas reductant being controlled by the open time for the injector. Atypical cycle time for the injector, i.e. the period between twoconsecutive openings of the injector, is preferably of the order of 0.5to 1.0 second.

The regulating parameters of the regulator depend inter alia on thecharacteristics of the high-pressure hose, such as its length anddiameter and the softness of its material, e.g. rubber. The regulatingparameters are also affected by temperature.

There are thus several characteristics which interact here and arecovered, from a regulating perspective, by the concept of hose rigidity.A difficulty is that the hose rigidity is unknown, e.g. at the time ofinstallation, and therefore needs somehow to be determined. One way ofdoing this is to manually calibrate the rigidity of every type of hosewhich might be relevant to the respective installation. However, this isvery time-consuming and involves problems, e.g. if hoses have to bechanged.

The object of the present invention is to simplify and improve thedetermination of hose rigidity so as not only to lead to less expensivehandling but also afford advantages pertaining to hose changing in thatno separate calibration need be done for each fresh hose.

SUMMARY OF THE INVENTION

According to the present invention, the hose rigidity B is calculatedand is thereafter used for calculating appropriate regulating parametersfor the pressure regulator, e.g. pressure. The regulator then calculatesthe control signal for the pump on the basis of these regulatingparameters.

The advantage of the device according to the present invention is nothaving to manually calibrate the regulator with respect to the rigidityof the high-pressure hose. This eliminates a calibration operationduring new production, changing of high-pressure hoses or restructuringof installations, and on the occasion of replacement of the controlunit.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic block diagram illustrating the present invention.

FIG. 2 comprises various graphs illustrating the present invention.

FIG. 3 is a flowchart illustrating the method according to the presentinvention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

The invention is described below in detail with reference to theattached drawings.

FIG. 1 is a schematic block diagram illustrating a pump system whichcomprises a pump, a tank, an injector with a pressure sensor and apressure regulator with an undepicted calculation unit. The pump isconnected to the injector by a high-pressure hose, hereinafter called“hose”, to transfer liquid to the injectors.

Surplus liquid is returned to the tank via a return hose, and liquidwhich is to be pumped out passes from a tank to the pump via a suctionhose. In the return hose, the liquid runs back to the tank, in which itis at approximately atmospheric pressure.

The regulator is adapted to control the pump by sending a control signalto the pump to pump liquid through the hose to the injector, which opensand closes in response to an injector control signal, and the time foran opening and closing cycle, called an injector cycle, is designatedT_(S) and the injector's open period is designated γ, where 0<γ<1 and 0denotes a situation in which the injector is closed for the wholeinjector cycle and 1 denotes a situation in which the injector is openfor the whole injector cycle.

The injector is provided with a pressure sensor adapted to measure thepressure of the liquid in the injector and to deliver a pressure sensorsignal to the calculation unit in the regulator, which calculation unitis adapted to determine on the basis of the pressure sensor signal thepressure amplitude A in the injector.

The calculation unit is further adapted to calculate the rigidity B ofthe hose as a function of the measured pressure amplitude A in theinjector, the injector cycle T_(S) and the injector's open period γ, andthe regulator is adapted to determine on the basis of B the controlsignal to the pump.

The control signal then regulates the pressure of the liquid which ispumped out by the pump. This regulation may for example take place insuch a way that if the hose has reached a rigidity value B whichindicates that the hose is more rigid, this represents a higher pressurethan if the hose rigidity indicates a less rigid hose. Moreover, alonger hose may require a higher pressure than a shorter hose. The hoselengths may vary greatly and may for example in the case of an SCRsystem be within the range of 1 to 25 meters. The double arrow to andfrom the regulator represents the connection to a superordinate system,e.g. an SCR system, which controls, and receives information from, theregulator. The injector control signal may be generated by the pressureregulator or by the superordinate system.

According to a preferred embodiment, the hose rigidity B is calculatedby the equation

${B = {\frac{1}{T_{S}}\frac{A}{\left( {1 - \gamma} \right)\gamma}}},$where 0<γ<1.

The hose rigidity B depends on one or more from among the length anddiameter of the hose and its material, which may for example be rubber.

The pump system according to the present invention is particularlysuited to use in an SCR system for a vehicle in which the liquid is forexample anhydrous ammonia, water-dissolved ammonia or urea, e.g. AdBlue.

The regulator is adapted to control the pump with respect to thepressure in the liquid which is pumped out, and in particular in orderto pump liquid at high pressure, the pressure of the liquid in the hosebeing for example of the order of 10 bar, i.e. 1 MPa.

The pump system according to the invention is preferably constantlyactivated, which means that the regulator continuously receives pressuresensor signals from the injector and can therefore automatically, i.e.in real time and continuously, adapt the pressure in the hose. Thesystem thus accounts for changes in the hose rigidity B caused by, forexample, changes in the temperature of the liquid. The pressure sensorsignals are taken up at a sampling frequency which is related to theinjector cycle. If the injector cycle is of the order of 1 second, thesampling frequency has to be at least 10 Hz, and preferably of the orderof 100 Hz, to achieve sufficient accuracy.

The present invention relates also to a method in a pump system,comprising causing a pump to pump a liquid through a hose to an injectorwhich is adapted to:

open and close with an open period designated γ and a time for the wholeopening and closing cycle which is designated T_(S);

measuring the pressure of the liquid in the injector;

calculating the rigidity B of the hose as a function of measuredpressure amplitudes A in the injector, the injector cycle T_(s) and theinjector's open period γ, and

determining on the basis of B the control signal to the pump.

The hose rigidity B is calculated by the equation

${B = {\frac{1}{T_{S}}\frac{A}{\left( {1 - \gamma} \right)\gamma}}},$where 0<γ<1.

When the system is in operation, the injector opens and closes in acontrolled way. This results in pressure pulsations in the high-pressurehose which are measured by the pressure sensor in the injector. FIG. 2is a schematic diagram of the possible form of such pressure pulsations,for a short hose (upper graph) and a long hose (lower graph). The top ofthe diagram represents the control signal to the injector. As may beseen in the diagram, the pressure drops when the injector is open andrises when the injector is closed. In the diagram, the injector is openfor an equally long time for both hoses, but the pressure pulsations areclearly of different amplitudes. A long hose results in smalleramplitudes than a short hose of the same type. In the example depicted,γ is approximately 0.25, i.e. the injector is open for a quarter of theinjector cycle T_(s).

It is thus possible to determine the rigidity of the hose by measuringthe following two magnitudes:

-   -   The proportion of the opening/closing cycle T_(s) for which the        injector is open, which proportion is designated γ and is        therefore between 0 and 1.    -   The amplitude A of the pressure pulsations.

The first and second magnitudes are known and come from thesuperordinate system, the third magnitude is calculated in thecalculation unit on the basis of the pressure signal. This takes placewith a slight delay of the order of one opening/closing cycle T_(s). Thehose rigidity B (which may have the same dimensions as forpressure/time) can then be determined by the above equation.

The derivation of this equation starts from a physical relationship (adifferential equation) which describes the pressure in the high-pressurehose. The physical relationship comprises the hose rigidity B and can beused to describe the slope of the pressure flanks. By equating themeasured slope in FIG. 2 with the slope resulting from the physicalrelationship it is possible to determine B according to the aboveexpression. A complete derivation of the equation for B appears at theend of the detailed description.

The hose rigidity B is then used to calculate appropriate regulatingparameters in the regulator in FIG. 1. The hose rigidity is normallyconstant for a given hose, but may vary with, for example, temperature.

There follows below a derivation of the equation for the hose rigidity Bwhich is used by the pump system according to the present invention.

To determine optimum regulator parameters for the pump regulator, it isnecessary to know the system's time constant τ. The time constant τvaries with the dosage γ. The τ values vary also across different typesof hose. It is therefore appropriate to determine τ by means of systemidentification while the system is in operation. We describe below how asuitable value of r can be calculated during operation.

The pressure in the system is described by the differential equation

$\begin{matrix}{\overset{.}{p} = {\frac{\beta}{V}\left\lbrack {{q(\chi)} - {{C_{q}\left( {a_{drain} + {\gamma\; a_{dos}}} \right)}\sqrt{\frac{2p}{\rho}}}} \right\rbrack}} & {{eq}.\mspace{14mu} 1}\end{matrix}$in which β and V respectively denote the hose's elasticity and volume,q(χ) the flow from the pump as a function of its control signal, and

${C_{q}\left( {a_{drain} + {\gamma\; a_{dos}}} \right)}\sqrt{\frac{2p}{\rho}}$the flow out from the high-pressure hose (via the return hose and thedosing valve).

Linearisation of equation 1 about p=p₀, produces

$\begin{matrix}{{{\frac{V}{\beta}\frac{\sqrt{2\rho\; p_{0}}}{C_{q}\left( {a_{drain} + {\gamma\; a_{dos}}} \right)}\overset{.}{p}} + p} = {{{q(\chi)}\frac{\sqrt{2\rho\; p_{0}}}{C_{q}\left( {a_{drain} + {\gamma\; a_{dos}}} \right)}} - p_{0}}} & {{eq}.\mspace{14mu} 2}\end{matrix}$

We also assume that the flow function q(χ) can be linearised about χ=χ₀(where χ₀ is the value of the control signal required to keep thepressure at p=p₀). The linearised flow function is

$\begin{matrix}{{q(\chi)} = {{{q\left( \chi_{0} \right)} + \frac{\partial q}{\partial\chi}}❘_{\chi_{0}}\left( {\chi - \chi_{0}} \right)}} & {{eq}.\mspace{14mu} 3}\end{matrix}$in which q(χ₀) can be calculated by equation 1 and by assuming thatequilibrium prevails, i.e. that the pressure is p₀:

$\begin{matrix}{{q\left( \chi_{0} \right)} = {{C_{q}\left( {a_{drain} + {\gamma\; a_{dos}}} \right)}\sqrt{\frac{2p_{0}}{\rho}}}} & {{eq}.\mspace{14mu} 4}\end{matrix}$

Inserting equation 4 in equation 3 produces

$\begin{matrix}{{q(\chi)} = {{{{C_{q}\left( {a_{drain} + {\gamma\; a_{dos}}} \right)}\sqrt{\frac{2p_{0}}{\rho}}} + \frac{\partial q}{\partial\chi}}❘_{\chi_{0}}\left( {\chi - \chi_{0}} \right)}} & {{eq}.\mspace{14mu} 5}\end{matrix}$

Inserting equation 5 in equation 2 then produces

$\begin{matrix}{{{\frac{V}{\beta}\frac{\sqrt{2\rho\; p_{0}}}{C_{q}\left( {a_{drain} + {\gamma\; a_{dos}}} \right)}\overset{.}{p}} + p} = {{\left( {{{{C_{q}\left( {a_{drain} + {\gamma\; a_{dos}}} \right)}\sqrt{\frac{2p_{0}}{\rho}}} + \frac{\partial q}{\partial\chi}}❘_{\chi_{0}}\left( {\chi - \chi_{0}} \right)} \right)\frac{\sqrt{2\rho\; p_{0}}}{C_{q}\left( {a_{drain} + {\gamma\; a_{dos}}} \right)}} - p_{0}}} & {{eq}.\mspace{14mu} 6}\end{matrix}$which may be simplified to

$\begin{matrix}{{{\frac{V}{\beta}\frac{\sqrt{2\rho\; p_{0}}}{C_{q}\left( {a_{drain} + {\gamma\; a_{dos}}} \right)}\overset{.}{p}} + \left( {p - p_{0}} \right)} = {{\frac{\sqrt{2\rho\; p_{0}}}{C_{q}\left( {a_{drain} + {\gamma\; a_{dos}}} \right)}\frac{\partial q}{\partial\chi}}❘_{\chi_{0}}\left( {\chi - \chi_{0}} \right)}} & {{eq}.\mspace{14mu} 7}\end{matrix}$

For the regulator we previously assumed that the pressure in the systembehaves like the first-order differential equationτ{dot over (p)}+(p−p ₀)=k(χ−χ₀)  eq. 8

With equations 7 and 8 it is now possible to identify the time constantτ as

$\begin{matrix}{\tau = {\frac{V}{\beta\; C_{q}}\frac{\sqrt{2\rho\; p_{0}}}{\left( {a_{drain} + {\gamma\; a_{dos}}} \right)}}} & {{eq}.\mspace{14mu} 9}\end{matrix}$

The expression for τ contains some unknown constants which have to bedetermined. We can do this by looking at the “sawtooth pattern”superimposed in the pressure signal when the system doses, asillustrated in FIG. 2.

We assume that:

-   -   the dosage is kept constant (i.e. γ=const)    -   the system's mean pressure is {tilde over (p)}=p₀    -   the flow through the pump is almost constant during the cycle        T_(s) (i.e. q(χ)=const).

On the above assumptions, {tilde over ({dot over (p)}=0, which makes itpossible to approximate q(χ) to

$\begin{matrix}{{q(\chi)} = {{C_{q}\left( {a_{drain} + {\gamma\; a_{dos}}} \right)}\sqrt{\frac{2p_{0}}{\rho}}}} & {{eq}.\mspace{14mu} 10}\end{matrix}$

We can express the derivative on the downward pressure flank of thesawtooth pattern as

$\begin{matrix}{{\overset{.}{p}}_{\downarrow} = {\frac{\beta}{V}\left\lbrack {{q(\chi)} - {{C_{q}\left( {a_{drain} + a_{dos}} \right)}\sqrt{\frac{2p}{\rho}}}} \right\rbrack}} & {{{eq}.\mspace{14mu} 11}a}\end{matrix}$(i.e. equation 1 with gamma=1)

Inserting equation 10 in equation 11a then produces equation 11.

We can now approximate the derivative on the downward pressure flank ofthe sawtooth pattern to

$\begin{matrix}{{\overset{.}{p}}_{\downarrow} = {\frac{\beta}{V}\left\lbrack {{{C_{q}\left( {a_{drain} + {\gamma\; a_{dos}}} \right)}\sqrt{\frac{2p_{0}}{\rho}}} - {{C_{q}\left( {a_{drain} + a_{dos}} \right)}\sqrt{\frac{2p_{0}}{\rho}}}} \right\rbrack}} & {{eq}.\mspace{14mu} 11}\end{matrix}$which may be simplified to

$\begin{matrix}{{\overset{.}{p}}_{\downarrow} = {{- \frac{\beta}{V}}C_{q}a_{dos}\sqrt{\frac{2p_{0}}{\rho}}\left( {1 - \gamma} \right)}} & {{eq}.\mspace{14mu} 12}\end{matrix}$

We can also approximate {dot over (p)}_(↓) from FIG. 2 to

$\begin{matrix}{{\overset{.}{p}}_{\downarrow} = {- \frac{2A}{\gamma\; T_{s}}}} & {{eq}.\mspace{14mu} 13}\end{matrix}$

If we equate equations 12 and 13, we arrive at the followingrelationship (after slight reorganisation):

$\begin{matrix}{A = {\frac{\beta}{V}C_{q}a_{dos}T_{s}\sqrt{\frac{p_{0}}{2\rho}}\left( {1 - \gamma} \right)\gamma}} & {{eq}.\mspace{14mu} 14}\end{matrix}$

For a given system this is an expression in the formA=BT _(s)(1−γ)γ,  eq. 15in which

$\begin{matrix}{B = {{\frac{\beta}{V}C_{q}a_{dos}\sqrt{\frac{p_{0}}{2\rho}}} = {const}}} & {{eq}.\mspace{14mu} 16}\end{matrix}$

The curve A(γ) is a parabola with zero points γ=0 and γ=1, and maxima atthe point (γ, A)=(0.5, 0.25BT_(s)). Using instantaneous values of A, γand T_(s) in the software makes it possible to determine the constant Bfrom equation 15:

$\begin{matrix}{B = \frac{A}{{T_{s}\left( {1 - \gamma} \right)}\gamma}} & {{eq}.\mspace{14mu} 17}\end{matrix}$

The unit of measure for B is Pa/s. A conceivable description for B is“pressure rate constant” or, more simply, “hose constant”.

When B has been determined, we can express the factor

$\frac{V}{\beta\; C_{q}}\sqrt{2\rho\; p_{0}}$in equation 9 (with the help of equation 16) as

$\begin{matrix}{{\frac{V}{\beta\; C_{q}}\sqrt{2\rho\; p_{0}}} = {a_{dos}p_{0}\frac{1}{B}}} & {{eq}.\mspace{14mu} 18}\end{matrix}$

Insertion in equation 9 produces

$\begin{matrix}{\tau = \frac{p_{0}}{B\left( {\frac{a_{drain}}{a_{dos}} + \gamma} \right)}} & {{eq}.\mspace{14mu} 19}\end{matrix}$

Knowledge of the system's time constant r is then usable in calculatingthe regulating parameters.

The present invention is not confined to the preferred embodimentsdescribed above. Sundry alternatives, modifications and equivalents maybe used. The above embodiments are therefore not to be regarded aslimiting the invention's scope of protection.

The invention claimed is:
 1. A method of controlling a pump system,comprising: based on a control signal sent to a pump, causing the pumpto pump a liquid through a hose to an injector which is configured toopen and close with an open period designated γ and a time for a wholeopening and closing cycle which is designated T_(S); measuring thepressure of the liquid in the injector; calculating the rigidity B ofthe hose as a function of measured pressure amplitudes A in theinjector, the injector cycle T_(S), and the injector's open period γ,and determining on the basis of B the control signal to the pump.
 2. Amethod according to claim 1, in which the hose rigidity B is calculatedby the equation${B = {\frac{1}{T_{s}}\frac{A}{\left( {1 - \gamma} \right)\gamma}}},$where 0<γ<1.
 3. A pump system, comprising: a pump, an injector, a hoseconnecting the pump to the injector, and an electronic pressureregulator, which regulator is configured to control the pump by sendinga control signal to the pump to cause the pump to pump a liquid throughthe hose to the injector which opens and closes in response to aninjector control signal, the time for an opening and closing cycle beingcalled an injector cycle and designated T_(S), and the injector's openperiod being designated γ, the injector cycle T_(S) and the injector'sopen period γ, being determined by the injector control signal, theinjector being provided with a pressure sensor configured to measure thepressure of the liquid in the injector and to deliver a pressure sensorsignal to the regulator, which regulator is configured to calculate, onthe basis of the pressure sensor signal, the pressure amplitude A in theinjector and to calculate the hose's rigidity B on the basis of thecalculated pressure amplitude A in the injector, the injector cycleT_(S) and the injector's open period γ, the regulator being configuredto determine, on the basis of the hose's rigidity B, the control signalsent to the pump.
 4. A pump system according to claim 3, in which thehose rigidity B is calculated by the equation${B = {\frac{1}{T_{s}}\frac{A}{\left( {1 - \gamma} \right)\gamma}}},$where 0<γ<1.
 5. A pump system according to claim 3, wherein said systemis configured for a vehicle's SCR system.
 6. A pump system according toclaim 3, wherein said system is configured to pump liquid at highpressure.
 7. A pump system according to claim 3, further comprising areturn hose, a tank and a suction hose intended to return liquid to thepump.
 8. A pump system according to claim 3, wherein the regulator isconfigured to control said pump with respect to the pressure of theliquid pumped out.
 9. A pump system according to claim 3, wherein thehose rigidity B depends on at least one of: (1) the length of the hose,(2) the diameter of the hose, and (3) the material of the hose.
 10. Apump system according to claim 3, wherein the liquid is urea.